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Scientific Investigations Report 2012–5116

Prepared in cooperation with the Chester County Water Resources Authority

A Benthic-Macroinvertebrate Index of Biotic Integrity and Assessment of Conditions in Selected Streams in Chester County, Pennsylvania, 1998–2009

By Andrew G. Reif

Thumbnail of and link to report PDF (24.7 MB)Abstract

The Stream Conditions of Chester County Biological Monitoring Network (Network) was established by the U.S. Geological Survey and the Chester County Water Resources Authority in 1969. Chester County encompasses 760 square miles in southeastern Pennsylvania and has a rapidly expanding population. Land-use change has occurred in response to this continual growth, as open space, agricultural lands, and wooded lands have been converted to residential and commercial lands. In 1998, the Network was modified to include 18 fixed-location sites and 9 flexible-location sites. Sites were sampled annually in the fall (October–November) during base-flow conditions for water chemistry, instream habitat, and benthic macroinvertebrates. A new set of 9 flexible-location sites was selected each year. From 1998 to 2009, 213 samples were collected from the 18 fixed-location sites and 107 samples were collected from the 84 flexible-location sites. Eighteen flexible-location sites were sampled more than once over the 12-year period; 66 sites were sampled only once.

Benthic-macroinvertebrate data from samples collected during 1998–2009 were used to establish the Chester County Index of Biotic Integrity (CC-IBI). The CC-IBI was based on the methods and metrics outlined in the Pennsylvania Department of Environmental Protection’s "A Benthic Index of Biotic Integrity for Wadeable Freestone Streams in Pennsylvania." The resulting CC-IBI consists of scores for benthic-macroinvertebrate samples collected from sites in the Network that related to reference conditions in Chester County.

Mean CC-IBI scores for 18 fixed-location sites ranged from 37.21 to 88.92. Thirty-nine percent of the 213 samples collected at the 18 fixed-location sites had a CC-IBI score less than 50; 33 percent, 50 to 70; 28 percent, greater than 70. CC-IBI scores from the 107 flexible-location samples ranged from 23.48 to 99.96. Twenty-five percent of the 107 samples collected at the flexible-location sites had a CC-IBI score less than 50; 33 percent, 50 to 70; and 42 percent, greater than 70.

Factors that were found to affect CC-IBI scores are nutrient concentrations, habitat conditions, and percent of wooded and urban land use. A positive relation was determined between mean CC-IBI scores and mean total habitat scores for the 18 fixed-location sites. CC-IBI scores were most strongly affected by stream bank vegetative protection, embeddedness, riparian zone width, and sediment deposition. The highest CC-IBI scores were associated with sites that had greater than 28 percent wooded-wetland-water land use, less than 5 percent urban land use, and no municipal wastewater discharges within 10 miles upstream from the sampling site. The lowest CC-IBI scores were associated with sites where urban land use was greater than 15 percent or a municipal wastewater discharge was within 10 miles upstream from the sampling reach.

The Mann Kendall test for trends was used to determine trends in CC-IBI scores and concentrations of nitrate, orthophosphate, and chloride for the 18 fixed-location sites. A positive trend in CC-IBI was determined for six sites, and a negative trend was determined for one site. Positive trends in nitrate concentrations were determined for 4 of the 18 fixed-location sites, and a negative trend in orthophosphate concentrations was determined for 1 of the 18 fixed-location sites. Positive trends in chloride concentrations were determined for 16 of the 18 fixed-location sites.

First posted September 19, 2012

  • Appendixes 1–4 XLSX (1731 KB)
    Appendix 1. Organisms with pollution tolerance values and references used in the Chester County Index of Biotic Integrity calculations
    Appendix 2. Chester County Index of Biotic Integrity scores, other index scores, and taxa counts for all samples collected as part of the Stream Conditions of Chester County Biological Monitoring Network, Pennsylvania, 1998–2009
    Appendix 3. Constituent concentrations in, and field characteristics of, streamwater samples collected as part of the Stream Conditions of Chester County Biological Monitoring Network, Chester County, Pennsylvania, 1998–2009
    Appendix 4. Total habitat assessment score and scores of individual habitat characteristics for all sites sampled as part of the Stream Conditions of Chester County Biological Monitoring Network, Chester County, Pennsylvania, 1998–2009

For additional information contact:
Director, Pennsylvania Water Science Center
U.S. Geological Survey
215 Limekiln Road
New Cumberland, PA 17070-2424
http://pa.water.usgs.gov/

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Suggested citation:

Reif, A.G., 2012, A benthic-macroinvertebrate index of biotic integrity and assessment of conditions in selected streams in Chester County, Pennsylvania, 1998–2009: U.S. Geological Survey Scientific Investigations Report 2012–5116, 41 p.



Contents

Abstract

Introduction

Purpose and Scope

Description of Network

Previous Investigations

Description of Study Area

Hydrologic Conditions

Sampling and Analytical Methods

Benthic Macroinvertebrates

Field Characteristics

Nutrients, Major Ions, and Metals

Habitat

Quality Control

Chester County Index of Biotic Integrity

Chester County Index of Biotic Integrity Metrics

Reference Condition

Chester County Index of Biotic Integrity Calculations

Assessment of Stream Conditions in Chester County, 1998–2009

Benthic Macroinvertebrates

Field Characteristics

Chemical Analysis

Nutrients

Major Ions and Metals

Habitat

Factors Affecting Chester County Index of Biotic Integrity Scores for 18 Fixed-Location Sites

Flow Conditions

Nutrients

Wastewater Discharges

Habitat Characteristics

Land Use

Evaluation of Chester County Index of Biotic Integrity Scores for Selected Flexible-Location Sites

Trends in Chester County Index of Biotic Integrity Scores and Selected Chemical Constituent Concentrations

Summary and Conclusions

References Cited

Appendix 1. Organisms with pollution tolerance values and references used in the Chester County Index of Biotic Integrity calculations

Appendix 2. Chester County Index of Biotic Integrity scores, other index scores, and taxa counts for all samples collected as part of the Stream Conditions of Chester County Biological Monitoring Network, Pennsylvania, 1998–2009

Appendix 3. Constituent concentrations in, and field characteristics of, streamwater samples collected as part of the Stream Conditions of Chester County Biological Monitoring Network, Chester County, Pennsylvania, 1998–2009

Appendix 4. Total habitat assessment score and scores of individual habitat characteristics for all sites sampled as part of the Stream Conditions of Chester County Biological Monitoring Network, Chester County, Pennsylvania, 1998–2009


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